Approximately two million cataract surgery procedures are performed in the United States annually. The procedure generally involves making an incision in the anterior lens capsule to remove the cataractous crystalline lens and implanting an intraocular lens in its place. The power of the implanted lens is selected (based upon pre-operative measurements of ocular length and corneal curvature) to enable the patient to see without additional corrective measures (e.g., glasses or contact lenses). Unfortunately, due to errors in measurement, and/or variable lens positioning and wound healing, about half of all patients undergoing this procedure will not enjoy optimal vision without correction after surgery. Brandser et al, Acta Ophthalmol Scand 75:162-165 (1997); Oshika et al., J. Cataract Refract Surg 24:509-514 (1998). Because the power of prior art intraocular lenses generally cannot be adjusted once they have been implanted, the patient typically must choose between replacing the implanted lens with another lens of a different power or be resigned to the use of additional corrective lenses such as glasses or contact lenses. Since the benefits typically do not outweigh the risks of the former, it is almost never done.
Recently, a new type of intraocular lens has been described which permits post-operative manipulation of the optical properties of the lens. This allows for post-operative adjustment of the lens to achieve optimal vision quality for the patient. The post-operative manipulation is accomplished through the polymerization of modifying composition (“MC”) in specific regions of the lens by external stimuli, such as light. By polymerizing the MC in specific regions, the optical qualities of the lens can be adjusted until the desired optical properties are achieved. To prevent further changes in the optical properties, however, any remaining MC is then polymerized throughout the lens, “locking-in” the properties.
Unfortunately, this prevents further adjustment of the lens at a later time. For example, if the lens were implanted in a child, it would not be possible to readjust the lens to compensate for changes in vision due to aging or the like. In this case, the patient would have to choose between surgery to replace the lens or to use other corrective devices, e.g., glasses.
Thus, a need exists for an intraocular lens whose optical properties can be adjusted on more than one occasion.